Potted plants aren't the answer to sick building syndrome

If you want to improve the quality of the air in your home or office, forget about buying a few indoor plants. You'd have to make the place look like the Palm House at Kew Gardens to have even the slightest impact, claims an Australian researcher.

A variety of organic molecules known as volatile organic compounds (VOCs) have been found in office air and linked to sick building syndrome, a range of symptoms that leaves people feeling tired, irritable and unwell but with no specific illness. Aside from obvious moves such as improving ventilation and removing sources of VOCs, potted plants have been touted as a potential solution to the problem-although evidence that they remove pollutants is sparse. "Everybody believes plants are the answer to sick buildings and indoor air pollution," says environmental scientist Peter Dingle of Murdoch University in Western Australia. "It's one of the great urban myths."

To test whether this particular myth had any basis in fact, Dingle and his colleagues examined the effects of plants on levels of formaldehyde, a toxic chemical that can irritate the eyes, skin and throat, and is thought to cause nausea, dizziness and lethargy at levels as low as 50 parts per billion (ppb). It may also aggravate asthma and hay fever and is a potential carcinogen.

Dingle and his colleagues measured formaldehyde levels in offices where the occupants had complained of poor air quality. As well as studying 18 office buildings in Perth, the researchers studied 20 temporary buildings on their university campus. These are typically built using major sources of formaldehyde-pressed wood products such as plywood and some types of foam insulation.
Average levels of formaldehyde ranged from 10 ppb to 78 ppb in the office buildings. But concentrations in the temporary cabins ranged from 420 ppb to 2110 ppb-far in excess of the WHO's safety standard of 82 ppb.

Dingle then set up five experimental cabins with a floor space of 8 square metres each. Into each, he placed five plants every two days until there were 20 plants in the cabin. With up to 10 plants in a cabin, formaldehyde concentrations remained unchanged. With 20 plants, average levels of formaldehyde were only reduced from 856 ppb to 761 ppb. If potted plants do help treat sick building syndrome, Dingle concludes, the effect is psychological. "They really make a place more comfortable and beautiful, but they do not clean the air of pollutants to any significant degree."

However, Jeff Llewellyn, an expert on indoor air quality with Britain's Building Research Establishment in Watford, says that the importance of such psychological factors shouldn't be underestimated. He also points out that the ability of plants to remove other pollutants hasn't been adequately studied: "Formaldehyde is but one pollutant."